Salivary Cortisol Responses and Session Ratings of Perceived Exertion to a Rugby Match and Fatigue Test

Abstract

This study compared the effects of an official rugby match and a fatigue test on the salivary cortisol responses of 13 rugby players. We also examined the relationship between this cortisol response and session ratings of perceived exertion (session-RPE). We collected saliva before and after the match and fatigue test and assessed physical effort intensity via session-RPE using a CR-10 scale. We measured cortisol concentration by enzyme-linked immunosorbent assays. Results were greater session-RPE and cortisol concentrations for the rugby match, compared with the fatigue test. There was a significant difference between cortisol concentrations obtained pre- and postmatch (p < .022) and significant correlations between cortisol response and session-RPE sampling in both the rugby match (r = .81; p < .001) and fatigue test (r = .91; p < .001). This study provides evidence of greater perceived effort and higher cortisol concentrations in actual competition versus a fatigue test. Our data further support session-RPE as a relatively inexpensive close correlate of a stress biomarker (cortisol response). Thus, session-RPE can be used by coaches as a valid indication of training loads and adequate recovery time after exertion.

Keywords

physical stressors exercise response rating of perceived exertion team performance human performance

Introduction

The impact of exercise- and sports-related stress on hormonal responses has been extensively studied by salivary biomarkers (Moreira et al., 2013; Papacosta & Nassis, 2011). Many salivary compounds can be derived from plasma by passive diffusion or active transport, making salivary assessment increasingly important in the fields of endocrinology, immunology, physiology, psychology, and sports medicine (Chiappin, Antonelli, Gatti, & De Palo, 2007; Chicharro, Lucía, Pérez, Vaquero, & Ureña, 1998; Humphrey & Williamson, 2001).

Saliva sampling has such distinct advantages over blood sampling as a lower risk of contamination and an easy, self-conducted, noninvasive collection procedure (Bonne & Wong, 2012; Caetano Júnior, Strixino, & Raniero, 2015). In addition, since salivary composition during exercise is influenced by the autonomic nervous system and the hypothalamic–pituitary–adrenal axis, and cortisol concentrations reflect plasma-free cortisol levels that are not altered by variations in flow rate (Stupnicki & Obminski, 1992; Vining McGinley, Maksujtis, & Ho, 1983), salivary cortisol concentrations are a good indication of the adrenocortical response to exercise.

During training programs, athletes are submitted to a wide range of stressors (physiological and psychological), and cortisol levels change with different forms of exercise. The daily training load has been considered the main physiological stress source, but official competitions emerge as potent psychological stressors as well, because competition is associated with novelty, ego involvement, anxiety, lack of control, and unpredictability (Buchanan, al’Absi, & Lovallo, 1999; Moreira et al., 2013; Rushall, 1990).

Physiological stress experienced by athletes has been investigated more often in individual sports than in team sports. Some studies showed that immediate postgame cortisol concentrations had significantly increased (Cunniffe et al., 2010; Elloumi, Maso, Michaux, Robert & Lac, 2013; Lindsay, Lewis, Scarrott, Draper & Gieseg, 2015). However, there is a particular lack of information about the physiological stress experience of rugby players in both the actual match environment and during training sessions. Yet, this knowledge is important for planning training and recovery time between successive games.

Despite the need for studies showing the salivary cortisol response in different types of physical effort, these laboratory tests are relatively expensive and laborious, making these data impossible for teams with limited financial support to access (Caetano Júnior, Lemes, Carvalho Aguiar, Strixino, & Raniero, 2016). Thus, many researchers have proposed an alternative, simpler method of assessing exercise intensity through subjective session ratings of perceived exertion (session-RPE; Foster, 1998; Foster et al., 2001). To the best of our knowledge, no studies have compared salivary cortisol responses and session-RPE from rugby players after fatigue test and official matches. Thus, this study aimed to assess the effects of an official rugby match and fatigue test on the salivary cortisol response and physical effort intensity measured by session-RPE in rugby players. In addition, we sought to examine the relationship between cortisol response and session-RPE to determine whether session-RPE might be a valid measurement tool for stress-related exercise intensity in these different types of physical effort.

Method

Participants

Thirteen rugby players participated voluntarily in this study (age: 19 ± 1 years; height: 174 ± 6 cm; body mass: 77.2 ± 12.2 kg). The rugby players trained twice a day (90–120 minutes per session), during five days per week (depending on the number of matches per week). All participants were informed of the benefits and risks of the study and provided written informed consent before participation. The study was approved by the Ethics Research Committee of the University of Vale of Paraiba, Brazil.

Procedure

The rugby players were evaluated over two weeks, during the competitive rugby season. All participants were instructed to maintain their normal dietary intake during the two weeks of testing. The rugby match studied in this experiment was composed of two 40 minute playing periods, separated by 10 minutes. The match was preceded by a 30 minute warm-up of stretching, running, and rugby drills. Players were encouraged to drink water ad libitum during break periods to maintain hydration levels. All players provided saliva samples 30 minutes before (∼14:30 h) and after (∼16:30 h) the official rugby match.

Three days after the match, the same players submitted to a fatigue test, performed on a treadmill (Movement LX 150). The players performed a warm-up for five minutes at a speed of seven km/h. The test protocol was performed as follows: the players were required to run at nine km/h for five minutes, followed by one km/h speed increments every two minutes until they achieved fatigue (Quammen et al., 2012), when they were instructed to signal with their arm at which point the speed was slowed to a walk. The saliva samples were collected pre (7:00 hours) and post-fatigue (∼7:30 hours) test.

Session Rating of Perceived Exertion

The physical effort intensity was assessed by session-RPE using a CR-10 scale as previously described by Foster (1998). This method is used as an indicator of exercise intensity for monitoring training and competition load. The data were collected 30 min after fatigue test and rugby match, when players answered a simple question—“How was your workout?.” For this, a chart was shown that outlined the full session-RPE (CR-10 scale) with the appropriate explanations.

Saliva Collection

The subjects provided saliva samples at 7:00 hours pre- and postfatigue test. The saliva collection was performed 30 minutes before the match warm-up (∼14:30 hours) and after match, where samples were collected within 10 minutes of the completion of the match (∼16:30 h). All subjects were informed in advance to abstain from food and caffeine products for at least two hours prior to the saliva collection. In addition, the players were instructed to rinse out their mouths with distilled water and remain seated with eyes open, head tilted slightly forward, and avoid orofacial movements (Chiappin et al., 2007; Moreira et al., 2013). Unstimulated saliva samples were collected in sterilized tubes (two ml) and immediately frozen and stored at −80℃ until assayed for cortisol concentration. The salivary cortisol concentrations were measured one week after the last collection of saliva.

Assays

The cortisol concentration was measured in duplicate using enzyme-linked immunosorbent assays (ELISA; Cortisol saliva; DIAsource ImmunoAssays SA, Louvain-Ia-Neuve, Belgium). Saliva samples were thawed and centrifuged at 1,630 grams for 20 minutes. After this process, 50 µl of each calibrator, control, and supernatant saliva samples were added to labeled wells (Rabbit anti-cortisol antibody coated microwell plate-break apart wells). The conjugate working solution (100 µl) was pipetted into each well and incubated for 45 minutes in a plate shaker (∼200 rpm), at room temperature (25℃). The plate was washed three times with 300 µl of diluted wash buffer per well. Then, 150 µl of tetramethylbenzidine substrate solution was added and again incubated on the plate shaker for 20 minutes, at room temperature (25℃). Finally, 50 µl of stooping solution was pipetted in each well, where a yellow color was obtained. The absorbance was read using a multimode microplate reader at 450 nm (Synergy HT, BioTek® Instruments, Inc. USA), within 20 minutes after the addition of the stopping solution. The cortisol concentration (ng/ml) of each sample was done from a calibration curve (absorbance vs. cortisol concentration of the calibrators).

Statistical Analyses

Data are reported as means and standard deviation (SD). Data distribution was assessed using the Kolmogorov–Smirnov test for normal distributions. A one-way analysis of variance with a post hoc test (Tukey) was used to compare the salivary cortisol concentrations and session-RPE. The level of significance was set at p < .05. The relationships between the cortisol concentrations and session-RPE were analyzed using Pearson's correlation coefficient.

Results

The mean scores obtained on session-RPE were 8.0 ± 1.8 and 7.6 ± 1.7 for the rugby match and fatigue test, respectively (Figure 1(a)). Statistical analyses showed no significant difference for session-RPE results in rugby match and fatigue test, F(1,46) = 0.315, p = .579. The perceived intensities of the rugby match for the sample (n = 13) was hard (three players), very hard (six players), and maximal (four players). The session-RPE’s of the same players regarding fatigue test intensity were hard (four players), very hard (eight players), and maximal (one player; Figure 1(b)). The achieved maximum time (minutes) at point of fatigue on the fatigue test was 14.7 ± 2.5 (mean ± SD).

Figure 1.

Session-RPE (mean ± SD) recorded after official rugby match and fatigue test (a). Session-RPE recorded after official rugby match and fatigue test per player (b).

Statistical analysis showed significant differences between salivary cortisol concentrations obtained before (26.0 ± 13.1) and after (41.5 ± 18.7) rugby match, F(1,46) = 5.913, p < .022, while for cortisol concentrations obtained pre- (31.2 ± 16.9) and postfatigue test (39.3 ± 18.3), no significant differences, F(1,46) = 2.614, p = .118, were found (Figure 2).

Figure 2.

Salivary cortisol concentrations (Mean ± SD) for rugby players in official rugby match and fatigue test (n = 13). *Significant difference between cortisol concentration collected pre- and postmatch (p < .05).

Variations of cortisol concentrations before and after the match per player are shown in Figure 3. Only two players (P6 and P10) showed a decrease in cortisol after physical effort, noted by negative values of variation in the rugby match and fatigue test. The variation of cortisol collected before and after the rugby match was higher compared with the treadmill fatigue test, except for Player 9. In rugby match, seven players (P2, P5, P8, P9, P11, P12, and P13) showed a variation of cortisol above 50%, while in the fatigue test only six players (P2, P5, P9, P11, P12, and P13) showed variation above 50%.

Figure 3.

Variation of salivary cortisol concentrations per player (P) before and after rugby match and fatigue test.

Figure 4(a) and (b) shows the relationship between session-RPE and variations of cortisol concentration (pre and post) for the official rugby match and fatigue test, respectively. Significant correlations were observed between salivary cortical response and session-RPE in both the rugby match (r = .81; p < .001) and the fatigue test (r = .91; p < .001).

Figure 4.

Pearson’s correlation coefficient between the session-RPE and variation of salivary cortisol for rugby match (a) and fatigue test (b).

Discussion

The cortisol response is considered a sensitive biomarker of “stress” that can scientifically identify a player’s physiological response to a rugby game (Hellhammer, Wüst, & Kudielka, 2009; Moreira et al., 2013). Thus, the aim this study was to assess the effect of an official rugby match on salivary cortisol response and on physical effort intensity as measured by session-RPE. These two variables were correlated to show that session-RPE is a valid marker of exercise intensity under a variety of conditions and situations.

According to the session-RPE data, the rugby match and fatigue test were both of high-intensity effort; however, the session-RPE for the match was higher than for the fatigue test. These findings may be explained by rugby match characteristics, involving common high-intensity running and impacts over long periods performed in the game, compared with the time in the fatigue test. In addition, several studies have shown that sessions scores increase as competition progresses to increasingly more challenging games and more prepared opponents (Impellizzeri, Rampinini, Coutts, Sassi, & Marcora, 2004; Moreira et al., 2012; Moreira et al., 2013).

The session-RPE is a response derived from various factors such as signals from peripheral working muscles and joints, central cardiovascular and respiratory functions, and the central nervous system (Borg, 1982). In real sports competitions, the psychological experience is an additional factor, leading to stress increases that combine with physical demands (Cunniffe et al., 2010; Cunniffe, Morgan, Baker, Cardinale, & Davies, 2015; Lindsay et al., 2015; Moreira et al., 2013). This psychological factor is influenced by pressure in official competition and further contributes to the higher session-RPE scores obtained in the rugby match, compared with the fatigue test.

As noted, selected biochemical markers of “stress” can provide data regarding a player’s physiological response over time, in intermittent sport and continuous exercise (Khaustova, Shkurnikov, Tonevitsky, Artyushenko, & Tonevitsky, 2010; Lindsay et al., 2015; Moreira et al., 2013). Some studies have shown significant changes in markers of muscle damage, inflammation, psychophysiological stress, and immune system function in players (Cunniffe et al., 2010; Khaustova et al., 2010; Smart, Gill, Beaven, Cook, & Blazevich, 2008; Takarada, 2003). In this study, salivary cortisol was used as a biomarker to verify physiological responses. When comparing cortisol levels before and after a rugby match and fatigue test, we found a significant increase in cortisol after the rugby game.

These results are similar to data reported in other studies showing greater cortisol concentrations to official basketball matches and to a final championship volleyball match compared with simulated training matches and regular season play, respectively. Prior authors explained these results high psychological stress in official matches including pressure to achieve optimal outcomes, an unpredictable environment, and ego involvement in the importance of the match (Moreira et al., 2012; Moreira et al., 2013).

Salivary composition during exercise is influenced by the autonomic nervous system and the hypothalamic–pituitary–adrenal axis, where glucocorticoids are released from the adrenal cortex, mainly cortisol, in response to stress (Passelergue & Lac, 1999). However, this response depends on factors such as exercise intensity and duration, rest intervals, exercise selection and sequence, repetition velocity, frequency (Gatti & De Palo, 2011; Kraemer & Ratamess, 2005), psychological factors (Moreira et al., 2013), physiological adaptations (Marin, Bolin, Campoio, Guerra, & Otton, 2013), individual variability, and time of day (Dickerson & Kemeny, 2004).

Individual variations of cortisol concentrations show the stress level per player, and this level of biochemical analysis provides an increased understanding of the unique effect of stress on each player, useful for monitoring each player's acute and chronic experience (Lindsay et al., 2015). These acutely high variations were recorded for seven rugby players with higher values observed in the match from six players and from the fatigue test in one. Though match intensity was not assessed through a heart rate monitor or Global Positioning System, the outcomes show that these players probably performed the most strenuous actions (high-intensity running, ruck, maul, tackle, hit-up, and scrum) during the game (Cunniffe et al., 2010; Lindsay et al., 2015). Additionally, psychological factors and time in the match may have increased their cortisol concentrations, as previously discussed.

Consistent with previous studies, these findings show that individual variability and acute changes of cortisol levels make cortisol response a sensitive biomarker for assessing acute psychophysiological stress (Elloumi et al., 2013; Lindsay et al., 2015). In this study, cortisol analyses showed a difference in the response of this hormone among a group of players subjected to different stress conditions. The high correlations of cortisol response to the session-RPE method of measuring physical stress in both game conditions and the fatigue test showed that the session-RPE can be used to monitor training and competition to avoid excess “stress.” These results are important because successful training must avoid the combination of excessive overload and inadequate recovery. When athletes do not sufficiently respect the balance between training and recovery, nonfunctional overreaching and overtraining syndrome can occur, decreasing athletic performance (Meeusen et al., 2013) and creating serious health risks.

Footnotes

Article Notes

References

Bonne

N. J.

Wong

D. T.

(2012) Salivary biomarker development using genomic, proteomic and metabolomic approaches. Genome Medicine 4: 82.

Borg

G. A.

(1982) Psychophysical bases of perceived exertion. Medicine & Science in Sports & Exercise 14: 377–381.

Buchanan

T. W.

Al’Absi

Lovallo

W. R.

(1999) Cortisol fluctuates with increases and decreases in negative affect. Psychoneuroendocrinology 24: 227–241.

Caetano Júnior

P. C.

Lemes

L. C.

Carvalho Aguiar

Strixino

J. F.

Raniero

(2016) Application of FT-IR spectroscopy to assess physiological stress in rugby players during fatigue test. Research on Biomedical Engineering 32: 123–128.

Caetano Júnior

P. C.

Strixino

J. F.

Raniero

(2015) Analysis of saliva by Fourier transform infrared spectroscopy for diagnosis of physiological stress in athletes. Research on Biomedical Engineering 31: 116–124.

Chiappin

Antonelli

Gatti

De Palo

E. F.

(2007) Saliva specimen: A new laboratory tool diagnostic and basic investigation. Clinica Chimica Acta 383: 30–40.

Chicharro

J. L.

Lucía

Pérez

Vaquero

A. F.

Ureña

(1998) Saliva composition and exercise. Sports Medicine 26: 17–27.

Cunniffe

Hore

A. J.

Whitcombe

D. M.

Jones

K. P.

Baker

J. S.

Davies

(2010) Time course of changes in immuneoendocrine markers following an international rugby game. European Journal of Applied Physiology 108: 113–122.

Cunniffe

Morgan

K. A.

Baker

J. S.

Cardinale

Davies

(2015) Home versus away competition: Effect on psychophysiological variables in Elite Rugby Union. International Journal of Sports Physiology and Performance 10: 687–694.

10.

Dickerson

S. S.

Kemeny

M. E.

(2004) Acute stressors and cortisol responses: A theoretical integration and synthesis of laboratory research. Psychological Bulletin 130: 355–391.

11.

Elloumi

Maso

Michaux

Robert

Lac

(2003) Behaviour of saliva cortisol [C], testosterone [T] and the T/C ratio during a rugby match and during the post-competition recovery days. European Journal of Applied Physiology 90: 23–28.

12.

Foster

(1998) Monitoring training in athletes with reference to overtraining syndrome. Medicine & Science in Sports & Exercise 30: 1164–1168.

13.

Foster

Florhaug

J. A.

Franklin

Gottschall

Hrovatin

L. A.

Parker

Dodge

(2001) A new approach to monitoring exercise training. Journal of Strength and Conditioning Research 15: 109–115.

14.

Gatti

De Palo

E. F.

(2011) An update: Salivary hormones and physical exercise. Scandinavian Journal of Medicine & Science in Sports 21: 157–169.

15.

Hellhammer

D. H.

Wüst

Kudielka

B. M.

(2009) Salivary cortisol as a biomarker in stress research. Psychoneuroendocrinology 34: 163–171.

16.

Humphrey

S. P.

Williamson

R. T.

(2001) A review of saliva: Normal composition, flow, and function. Journal of Prosthetic Dentistry 85: 162–169.

17.

Impellizzeri

F. M.

Rampinini

Coutts

A. J.

Sassi

Marcora

S. M.

(2004) Use of RPE-based training load in soccer. Medicine & Science in Sports & Exercise 36: 1042–1047.

18.

Khaustova

Shkurnikov

Tonevitsky

Artyushenko

Tonevitsky

(2010) Noninvasive biochemical monitoring of physiological stress by Fourier transform infrared saliva spectroscopy. Analyst 135: 3183–3192.

19.

Kraemer

W. J.

Ratamess

N. A.

(2005) Hormonal responses and adaptations to resistance exercise and training. Sports Medicine 35: 339–361.

20.

Lindsay

Lewis

Scarrott

Draper

Gieseg

S. P.

(2015) Changes in acute biochemical markers of inflammatory and structural stress in rugby union. Journal of Sports Science 33: 882–891.

21.

Marin

D. P.

Bolin

A. P.

Campoio

T. R.

Guerra

B. A.

Otton

(2013) Oxidative stress and antioxidant status response of handball athletes: Implications for sport training monitoring. International Immunopharmacology 17: 462–470.

22.

Meeusen, R., Duclos, M., Foster, C., Fry, A., Gleeson, M.Nieman, D.,…European College of Sport Science, & American College of Sports Medicine. (2013). Prevention, diagnosis, and treatment of the overtraining syndrome: Joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. Medicine & Science in Sports & Exercise, 45, 186–205.

23.

Moreira

Crewther

Freitas

C. G.

Arruda

A. F.

Costa

E. C.

Aoki

M. S.

(2012) Session RPE and salivary immune-endocrine responses to simulated and official basketball matches in elite young male athletes. Journal of Sports Medicine and Physical Fitness 52: 682–687.

24.

Moreira

Freitas

C. G.

Nakamura

F. Y.

Drago

Aoki

M. S.

(2013) Effect of match importance on salivary cortisol and immunoglobulin A responses in elite young volleyball players. Journal of Strength and Conditioning Research 27: 202–207.

25.

Papacosta

Nassis

G. P.

(2011) Saliva as a tool for monitoring steroid, peptide and immune markers in sport and exercise science. Journal of Science and Medicine in Sport 14: 424–434.

26.

Quammen

Cortes

Van Lunen

B. L.

Lucci

Ringleb

S. I.

Onate

(2012) Two different fatigue protocols and lower extremity motion patterns during a stop-jump task. Journal of Athletic Training 47: 32–41.

27.

Passelergue

Lac

(1999) Saliva cortisol, testosterone and T/C ratio variations during a wrestling competition and during the post competitive recovery period. International Journal of Sports Medicine 20: 109–113.

28.

Rushall

B. S.

(1990) A tool for measuring stress tolerance in elite athletes. Journal of Applied Sport Psychology 2: 51–66.

29.

Smart

Gill

N. D.

Beaven

C. M.

Cook

C. J.

Blazevich

A. J.

(2008) The relationship between changes in interstitial creatine kinase and game-related impacts in rugby union. British Journal of Sports Medicine 42: 198–201.

30.

Stupnicki

Obminski

(1992) Glucocorticoid response to exercise as measured by serum and salivary cortisol. European Journal of Applied Physiology 65: 546–549.

31.

Takarada

(2003) Evaluation of muscle damage after a rugby match with special reference to tackle plays. British Journal of Sports Medicine 37: 416–419.

32.

Vining

R. F.

Mcginley

R. A.

Maksujtis

J. J.

K. Y.

(1983) Salivary cortisol: A better measure of adrenal cortical function than serum cortisol. Annals of Clinical Biochemistry 20: 329.